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Laura P Pardon, Faith M McAllister, Ronald S Harwerth, Nimesh Bhikhu Patel; The effects of short-term intraocular pressure elevation on the optic nerve head. Invest. Ophthalmol. Vis. Sci. 2018;59(9):2104.
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© ARVO (1962-2015); The Authors (2016-present)
Optic nerve head (ONH) neural rim tissue thickness, quantified as minimum rim width (MRW), is a sensitive measure for assessing optic neuropathies. An elevation of intraocular pressure (IOP) temporarily decreases MRW, however, the time course over which MRW decreases with an increase in IOP remains unknown. The goal of the present study was to investigate the dynamics of MRW over a two-hour period of mild-to-moderate elevation, and subsequent recovery, in non-human primate eyes.
Three healthy anesthetized adult non-human primates (Macaca Mulatta) were used for this study. A 27G needle was inserted into the anterior chamber of one eye of each animal; the needle was attached to a closed loop system that included a pressure transducer and syringe pump to set and maintain a steady IOP. For each eye, in two different sessions separated by a minimum of two weeks, IOP was maintained at either 25 mmHg or 40 mmHg for 2 hours and was then reduced to 10 mmHg for 2 additional hours. During each session, optical coherence tomography scans were obtained every 5 min. MRW was calculated using radial scans centered on the ONH. The MRW as a function of time was fit with an exponential decay or exponential rise to maximum function.
The maximum MRW thinning from baseline following 2 hours of elevated IOP was 37.4 µm (34.4- 67.9 µm) with 25 mmHg or 49.6 µm (46.2-65.7 µm) with 40 mmHg. The half-life for MRW reduction was 23.4 min (18.5-35.1 min) for the 25 mmHg sessions and 21.9 min (20.2 to 22.1 min) for 40 mmHg. Following elevation to 25 mmHg and subsequent reduction to 10 mmHg for 2 hours, residual MRW thinning was 29.8 µm (22.6-52.2 µm); residual thinning for the 40 mmHg sessions was 36 µm (32-36.4 µm). Although there was residual thinning after 2 hours at 10 mmHg, in all cases the MRW had recovered in the 2-4 week period between sessions.
The ONH neural rim tissue is sensitive to IOP, with MRW decreasing over an extended period during sustained mild-to-moderate IOP elevation. MRW does not recover to baseline at the same rate, however, the final full recovery of MRW demonstrates that the IOP-induced thinning is not due to axonal loss. The slow recovery of MRW following IOP reduction is an important factor to consider in glaucoma management and research involving the effects of IOP on the ONH.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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